(1) Field of the Invention
The present invention relates to an apparatus for transferring electric charges and, more particularly, relates to an apparatus for transferring electric charges in which the transferring electrodes are constituted by a plurality of transferring electrodes which are adjoined together in a charge transfer direction and a plurality of pairs of the electrodes are arranged along the transfer direction.
(2) Background of the art
Solid-state image sensing devices including charge coupled devices (CCDs) have been used for photographic elements in video cameras, still cameras, and so forth.
A structure of output ports for horizontal (output) register portions in these image sensing devices has been proposed.
It is necessary to enhance transferring efficiency in a transferring apparatus such as the horizontal register since the output dynamic range of the output register must be widened to some degree. It is not easy to achieve both enhanced transferring efficiency and widened output dynamic range.
In other words, to provide a sharp (clearly focused, high resolution) video image with high transferring efficiency, it is necessary to deepen a whole potential of a charge transferring channel to raise a potential relative to a zero potential). However, to deepen the whole potential is to narrow the dynamic range of a floating diffusion region. The floating diffusion region denotes an n.sup.++ type semiconductor region disposed at a position corresponding to a lower side of the output port of the output register downstream of an output port electrode.
That is to say, since the dynamic range of the floating diffusion region is determined according to a difference between the potentials of the dynamic range of the floating diffusion region and that of the output gate electrode, the potential difference becomes correspondingly smaller if the potential at the output gate electrode side is deepened. Hence, it is difficult to enhance the transferring efficiency without narrowing the dynamic range.
If the potential of the floating diffusion region is deepened, the output dynamic range can be widened. However, it becomes necessary to make higher the power supply voltage applied to a precharge drain region. The precharge drain region denotes an n.sup.++ type semiconductor region formed on a surface portion of the n type semiconductor region at a position slightly downstream and spaced apart from the floating diffusion region. If the power supply voltage (Vdd) is increased, an amplifier (the amplifier which detects and amplifies the potential of the floating diffusion electrode) would largely consume the power and would make the drain voltage applied to an MOS (Metal Oxide Semiconductor) transistor constituting the amplifier higher, to a value equal to or nearly equal to the breakdown voltage that the MOS transistor inherently provides.